Add Media Router Mojo impl code.

chrome/browser/media/router/media_router_mojo_impl_factory.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/media/router/media_router_mojo_impl_factory.h"
+
+#include "chrome/browser/media/router/media_router_mojo_impl.h"
+#include "components/keyed_service/content/browser_context_dependency_manager.h"
+#include "extensions/browser/process_manager_factory.h"
+
+using content::BrowserContext;
+
+namespace media_router {
+
+// static
+MediaRouterMojoImpl* MediaRouterMojoImplFactory::GetApiForBrowserContext(
+    BrowserContext* context) {
+  DCHECK(context);
+
+  return static_cast<MediaRouterMojoImpl*>(
+      GetInstance()->GetServiceForBrowserContext(context, true));
+}
+
+// static
+MediaRouterMojoImplFactory* MediaRouterMojoImplFactory::GetInstance() {
+  return Singleton<MediaRouterMojoImplFactory>::get();

[Wez, 2015/05/20 23:37:49]

I'm not familiar with this pattern; is this the preferred mechanism over
base::LazyInstance? I notice that the Singleton header cautions against using it
unless you absolutely have to... ;)

[imcheng (use chromium acct), 2015/05/21 19:28:52]

Done.

+}
+
+MediaRouterMojoImplFactory::MediaRouterMojoImplFactory()
+    : BrowserContextKeyedServiceFactory(
+          "MediaRouterMojoImpl",
+          BrowserContextDependencyManager::GetInstance()) {
+  DependsOn(extensions::ProcessManagerFactory::GetInstance());

[Wez, 2015/05/20 23:37:49]

nit: Consider documenting why we depend on this, since we don't seem to actually
call into it anywhere here! e.g. does the Impl() depend on it?

[imcheng (use chromium acct), 2015/05/21 19:28:52]

Done.

+}
+
+MediaRouterMojoImplFactory::~MediaRouterMojoImplFactory() {
+}
+
+KeyedService* MediaRouterMojoImplFactory::BuildServiceInstanceFor(
+    BrowserContext* context) const {
+  return new MediaRouterMojoImpl();
+}
+
+BrowserContext* MediaRouterMojoImplFactory::GetBrowserContextToUse(
+    BrowserContext* context) const {
+  // This means MediaRouterImpl is available in incongnito contexts as well.

[Wez, 2015/05/20 23:37:50]

typo: Incognito

This comment doesn't make clear what "this" is - are you saying that returning
the supplied |context| somehow makes it available to Incognito..?

[imcheng (use chromium acct), 2015/05/21 19:28:52]

I tried to clarified the comment. It just means we don't redirect incognito
context to the original context.

+  return context;
+}
+
+}  // namespace media_router